Primitive andesites from the Taupo Volcanic Zone formed by magma mixing

Beier, Christoph, Haase, Karsten M., Brandl, Philipp A. and Krumm, Stefan H. (2017) Primitive andesites from the Taupo Volcanic Zone formed by magma mixing Contributions to Mineralogy and Petrology, 172 (5). Art.No. 33. DOI 10.1007/s00410-017-1354-0.

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Supplementary data:

Abstract

Andesites with Mg# >45 erupted at subduction zones form either by partial melting of metasomatized mantle or by mixing and assimilation processes during melt ascent. Primitive whole rock basaltic andesites from the Pukeonake vent in the Tongariro Volcanic Centre in New Zealand’s Taupo Volcanic Zone contain olivine, clino- and orthopyroxene, and plagioclase xeno- and antecrysts in a partly glassy matrix. Glass pools interstitial between minerals and glass inclusions in clinopyroxene, orthopyroxene and plagioclase as well as matrix glasses are rhyolitic to dacitic indicating that the melts were more evolved than their andesitic bulk host rock analyses indicate. Olivine xenocrysts have high Fo contents up to 94%, δ18O(SMOW) of +5.1‰, and contain Cr-spinel inclusions, all of which imply an origin in equilibrium with primitive mantle-derived melts. Mineral zoning in olivine, clinopyroxene and plagioclase suggest that fractional crystallization occurred. Elevated O isotope ratios in clinopyroxene and glass indicate that the lavas assimilated sedimentary rocks during stagnation in the crust. Thus, the Pukeonake andesites formed by a combination of fractional crystallization, assimilation of crustal rocks, and mixing of dacite liquid with mantle-derived minerals in a complex crustal magma system. The disequilibrium textures and O isotope compositions of the minerals indicate mixing processes on timescales of less than a year prior to eruption. Similar processes may occur in other subduction zones and require careful study of the lavas to determine the origin of andesite magmas in arc volcanoes situated on continental crust.

Document Type: Article
Keywords: Taupo Volcanic Zone, Primitive andesite, Magma mixing, Subduction zones, Crustal magmatic processes
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems > Marine Mineralische Rohstoffe
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1007/s00410-017-1354-0
ISSN: 0010-7999
Projects: Future Ocean
Date Deposited: 02 May 2017 06:38
Last Modified: 09 Jan 2018 10:50
URI: http://eprints.uni-kiel.de/id/eprint/37740

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